Pectin is a complex polysaccharide associated with plant cell walls. It consists of an alpha 1-4 linked polygalacturonic acid backbone intervened by rhamnose residues and modified with neutral sugar side chains and non-sugar components such as acetyl, methyl, and ferulic acid groups. The neutral sugar side chains, which include arabinan and arabinogalactans, are attached to the rhamnose residues in the backbone.
A significant amount of research on pectins has been carried out due to its importance as a food product, a dietary fiber and a component of cell walls in higher plants, and to the growing awareness of a number of pharmacological activities. Current methods of extracting pectin, however, do not produce pectins of sufficient quality for all such uses.
Conventional methods of pectin extraction require extended heating of the pectin-containing plant materials at sub-boiling temperatures (approximately 65-85° C.) in an acidic media (pH below 2.2) for 1 to 10 hours. These processes, however, have high residence times and energy requirements and may provide only a moderate yield (20-30%) of pectin using a counter-current process (i.e., a process using a number, n, of extraction stages with which the originating raw material goes to extraction stage #1, the originating pure water goes the stage #n, and for any stage #i, assuming 1<i<n, the liquid comes from stage i+1 while the solids come from stage i−1). Thus, since the acidic condition is aggressive, and since a considerable part of the pectin becomes exposed to the acidic condition repeatedly, the pectins often are degraded during the conventional extraction processes.
As will be appreciated by those skilled in the art, it is desirable to extract a pectin having as high a degree of polymerization (DP) as possible for as low a cost as possible. The selection of production conditions like solid/liquid ratio, acidity, temperature, etc. all effect these conflicting considerations. For example, in order to accomplish an even moderately high yield using conventional processes, extraction conditions must be aggressive. In addition, following the extraction, the solids-liquid separation should be as complete as possible because the liquid that is retained by the solids after the separation will be exposed to the aggressive extraction conditions for a second time (due to the counter-current extraction setup). For the separation to be as complete as possible, however, the viscosity of the liquid preferably should be low, which is accomplished either by separating at high temperature, separating with a low solids/liquid ratio, or a combination of both. Use of a high temperature in combination with a low pH, however, is detrimental to the pectin quality (e.g., its degree of polymerization). Conversely, a low solids/liquid ratio becomes costly because larger amounts of water need to be removed from the pectin either by evaporation or by distillation of alcohol. Thus, there remains a need for a cost-effective process for extracting pectins without compromising the quality of the extracted pectins.
In addition, it is also important that the final pectin is free from unwanted contaminants, including any residual presence of the acid (and its salts) that was used for extracting the pectin. Thus, there also is a need in the pectin manufacturing industry for cost-effective ways of reducing the residual presence of the acids that were added for the extraction.
Additional aspects will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.